Vitamin C Forum

Any adverse effects of replacement vitamin C will be discuseed here. Topics include kidney stones, gall stones, oxidation, etc.
We plan to move good discussions from the General Topics forum here for posterity.

Dad has his diabetes pretty well under control, but he has been getting some abnormal readings of late. He was reading (not sure where.. it was in a newspaper, but he cannot remember the source) that excessive levels of Vit C can cause erroneous readings in the regular blood glucose testers.

Do you have any information about this? Are you aware if it is a known problem? It would go a long way towards explaining some of his readings.

Christine

Apparently it might... I've been doing some looking, and on the FDA site..

Factors That Affect Glucose Meter Performance The accuracy of your test results depends partly on the quality of your meter and test strips and your training. Other factors can also make a difference in the accuracy of your results.

Other Substances. Many other substances may interfere with your testing process. These include uric acid (a natural substance in the body that can be more concentrated in some people with diabetes), glutathione (an "anti-oxidant" also called "GSH"), and ascorbic acid (vitamin C). You should check the package insert for each meter to find what substances might affect its testing accuracy, and discuss your concerns with your health care provider.

Unfortunately, they don't suggest what to do. From reading about the errors with the urine test, it seemed that Vit C caused false positives (glucose appeared to be present when it was not). The excerpt above from the FDA site notes that Vit C can cause errors with the blood meters, and I am assuming that it will similarly cause a reading higher than the actual reading (which is what seems to be the case with Dad).

They speak about checking each meter's package insert for info as to if Vit C will affect it... so perhaps Dad might need to change his meter. I don't know if there are any meters that do not have a Vit C sensitivity, however.

Range from before-meal glucose levels of 90 to 130 milligrams per deciliter (mg/dL); after-meal values of less than 180 mg/dL. Values can vary depending on physical activity, meals, and insulin administration. Normal value ranges may vary slightly among different laboratories.

Vitamin C blood levels range up to 1.5 mg/dl - so even if vitamin C were being counted by the blood analysis, the vitamin would only add a maximum of 1 to 2 percent to the reading.

Urine is a different animal because "replacement " (not excessive!) doses of vitamin C wind up in the urine, but since a) animals make these amounts all day long, and b) most blood tests are probably tested on laboratory animals, one would think the urine tests would be able to account or filter ascorbate by now.

Owen R. Fonorow, Orthomolecular NaturopathMy statements have not been evaluated by the Food and Drug Administration. Any product mentioned is not intended to diagnose, treat, cure or prevent any disease.”

I understand what you are getting at, but I'm thinking about it from a different angle.

The urine strips used to give false positives because both reagents used in the different strips (the copper reduction test that uses cupric sulfate, and the glucose oxidase test, which uses toluidine and glucose oxidase)reacted to Vit C as well as glucose.

The many of the blood glucose machines also use the glucose oxidase test to produce a color change that is then translated into a numerical reading. The thing is, I am not at all sure that 1mg/dl of Vit C causes the same level of reaction as 1mg/dl of glucose. If it does, then your theory is correct, and there should be at most a 1-2% difference. If, however, 1mg/dl of Vit C causes a stronger reaction, it may well be that each 1mg/dl in the blood shows up as being the same as 50, 60, 100 mg/dl of glucose.

Simple experiments could determine this, and it is hard to believe that such tests would be developed that didn't take into account "normal" blood leves of C? Especially if ANY laboratory animal testing was done.

Owen R. Fonorow, Orthomolecular NaturopathMy statements have not been evaluated by the Food and Drug Administration. Any product mentioned is not intended to diagnose, treat, cure or prevent any disease.”

In DIABETES CARE, VOLUME 22, NUMBER 7, JULY 1999 there appeared a letter by Dr. Donald R. Branch, PhD entitled “High-Dose Vitamin C Supplementation Increases Plasma Glucose”. This letter describes "one 49-year-old slight-to-moderately obese, but otherwise healthy, male Caucasian who was found on routine examination to have elevated fasting plasma glucose". The patient appeared to have normal glycated hemoglobin A1c and normal urine glucose. The patient was taking greater than 4,500 mg/day of Vitamin C prior to testing. After 1 week without Vitamin C, serum glucose of the patient fell within normal range. When the patient resumed Vitamin C, his glucose was again elevated. Upon stopping Vitamin C again, his glucose levels return to normal levels. The patient refused to stop taking Vitamin C, but did reduce to 1,500 mg/day. At this level, the patient showed that glucose remained within normal levels. This indicated that in at least one person, Vitamin C may have a detrimental effect on serum glucose.

I wonder if there are other people who may be similarly affected by Vitamin C. If so, what would the percentage of the population be? This letter has been widely referred to on the internet as demonstrating an undesirable side effect of Vitamin C. Is there any merit to Dr. Branch’s observation?

The question was whether or not high vitamin C affects the glucose test? Certainly the fellow in this paper registered higher glucose, but was the test measuring glucose or was the high vitamin C giving a false reading? If glucose, why wasn't it expelled in the urine? (Also, this isolated result contradicts quite a bit of early research references by Stone and Cheriasken about vitamin C consistently "lowering" blood sugar)

Owen R. Fonorow, Orthomolecular NaturopathMy statements have not been evaluated by the Food and Drug Administration. Any product mentioned is not intended to diagnose, treat, cure or prevent any disease.”

What a quandary. This seems to be one of those controversial questions without a consensus. Some claim Vitamin C does affect certain glucose tests and others claim the opposite. Some claim it is not the test but that Vitamin C causes glucose abnormalities, while others claim it doesn’t. However, most of the works with high dose Vitamin C are not what I would call high dose ( > 6,000 mg/dy ). The dosages have been no more than 2,000 mg/dy. The big exception was Dr Branch’s letter with 4,500 mg/dy in “Diabetes Care 1999”.

From what I’m seeing there are some glucose assays which are affected by Vitamin C. I’m inclined to believe that, in some but not all people, serum glucose may be adversely affected. Even though certain people are not affected, it does not necessarily mean that everyone should not be affected. Perhaps this could be attributed to genetic diversity.

I think anyone who takes more then 1,500 mg/dy of supplemental Vitamin C should have their blood glucose levels monitored by a professional lab at least once a year. If levels are found to be slightly elevated ( < 126 mg/dL ), additional tests for fasting insulin and hemoglobin A1C might be appropriate. Curtailing supplemental Vitamin C for a couple of weeks and retesting may be worthwhile. Many doctors are not aware that Vitamin C might affect serum glucose and/or glucose tests. Voice this concern to the doctor before starting prescription drugs for diabetes.

Urine tests for glucose are not a reliable means to access glucose status. There are too many variables which cause poor readings. I can think of at least 7 (see next post). These tests have gone out of favor many years ago and are rarely used today.

For those who might be interested here are a few links related to this subject:

1. Although the renal threshold for glucose in healthy adults corresponds to a plasma glucose concentration of >180 mg/dl (10 mmol/l), there is wide individual variation. Of particular importance are findings that adults, especially those with long-standing diabetes, may have substantial increases in this threshold, resulting in underestimation of the blood glucose level. Conversely, children and, particularly, pregnant women may have very low or variable renal thresholds, resulting in overestimation of the blood glucose level.

2. Fluid intake and urine concentration affect urine test results.

3. The urine glucose value reflects an average level of blood glucose during the interval since the last voiding and not the level at the time of the test.

4. A negative urine glucose test does not distinguish between hypoglycemia, euglycemia, and mild or moderate hyperglycemia. Thus, urine glucose testing is of limited value in preventing hypoglycemia and hyperglycemia.

5. Urine glucose testing, which uses a color chart with which the test strip color is compared, is less accurate than capillary blood glucose monitoring, which typically uses a digital readout from a reflectance meter.

6. Some drugs interfere with urine glucose determinations.

7. Evaluation of urine dipsticks reveals high imprecision at low glucose concentrations. Manufacturers claim that the test strips are positive if urinary glucose concentrations are 100 mg/dl or greater, but the data indicate this does not always occur.

I've have been consuming 15,000 mg to 20,000 mg of vitamin C, mostly as ascorbic acid, since 1986 - 20 years. During that period, glucose levels in all of my blood tests have been normal, from memory, between 80 and 90 mg/dl. (No adverse readings in urine tests either.)

Owen R. Fonorow, Orthomolecular NaturopathMy statements have not been evaluated by the Food and Drug Administration. Any product mentioned is not intended to diagnose, treat, cure or prevent any disease.”

Are you claiming that it can not be possible for anyone to experience serum glucose increases from high doses of Vitamin C? We are not talking about very large excursions of glucose. An increase from 5.5 mmol/l to 6.6 mmol/l while worrisome may not be all that huge. I know of people whose fasting glucose exceeds 11.1 mmol/l but definately not from VC. I just find it difficult to believe that, while most people do very well on high doses of VC, certain individuals can experience increases in glucose levels. I suppose that I’m trying to find more definitive evidence for this supposition one way or the other. I apologize for being so troublesome, but at this time, it is very important to me.